The control of neuroendocrine release involves the blood as a vehicle for transporting messengers. For example, factors which regulate the synthesis and release of adenohypophyseal hormones are secretes by the median eminence and transported to the adenohypophysis by blood. The concentration of regulatory factors in adenohypophyseal blood is dependent on the rate of secretion of the factors by the median eminence and the rate of blood flow. Although pituitary blood flow is an important aspect in the regulation of pituitary function,it has not been adequately studied and is therefore not well understood. One reason for this limited understanding is that most existing techniques for measuring blood developed flow in the neurohypophysis using [14C] isopropyliodoamphetamine has been developed in our laboratory. This technique does not have the limitations of the existing techniques . Furthermore, it has capacity to measure regional neurohypophyseal blood flow in awake, freely-ranging, unstressed state. The local,neural, and hormonal control of neurohypophyseal blood flow will be studied during hypercapnia, hypoxia, and hypoglycemia. In addition, oxygen consumption will be measured in the neurohypophyseal in order to determine if neurohypophyseal blood flow is regulated primarily for the control of neuroendocrine release through the regulation of neurohypophyseal blood flow. Long-term objectives are different neuroendocrine states in order to fully understand how blood flow regulates neuroendocrine release.